As is well known, a pixel is a picture element on a computer display which has a certain color. Each logical pixel is actually formed of data defining 3 pixels, a red, green and blue pixel, each of which results in a visually merged, colored point on the display. In this disclosure, the term pixel will mean one logical pixel, that is, one set of red, green and blue elements defined by data.
A frame buffer is a memory which contains one frame of pixels, a frame being the total number of pixels that can be displayed on a display. VGA monitors have displays with a frame size of 640 by 480 pixels, and therefore a VGA frame buffer is a memory capable of holding 640×480, or 307,200 pixels.
While a pixel can be stored digitally using any number of bits, a standard “true color” display utilizes 24 bits per pixel, 8 bits for each red, green and blue color of each pixel. Another standard is 8 bits per pixel.
Many systems exist for controlling computer displays, but all systems employ separate integrated circuits for a graphics processor, a frame buffer, and pixel logical operations. The graphics processor can be a single chip or multiple chips interconnected to perform the required processing function. The frame buffer is typically made up of multiple video random access memory (VRAM) chips, or dynamic random access memory (DRAM) chips, as well as a memory controller chip. The pixel logic usually consists of some high speed logic, a high speed static random access memory (SRAM) chip, and a triple random access memory—digital to analog converter (RAMDAC) chip.
One of the critical tasks of a display controller system is to perform the graphics operations as quickly as possible. Bottlenecks determine the maximum speed of the system. One of the major bottlenecks in a graphics system is the interface throughput between the graphics processor and the frame buffer memory. The width of the bus between these two systems is proportional to the speed at which the system can process pixels (pixels per second). Most current systems have a 16 bit or a 32 bit interface, and the most powerful current system has a 64 bit interface.
Another major bottleneck is between the graphics processor and the RAMDAC. The power consumed in driving the capacitive loads of these two interfaces represents a significant fraction of overall graphics sub-system power.